The present invention relates to an olefin polymer resin composition which has improved electroconductivity and excellent processability and which comprises an olefin polymer resin, an electroconductive carbon black and an amide compound. The present invention also relates to foamable compositions and foamed articles prepared from said olefin polymer resin composition.
It is well known to obtain an electroconductive resin by mixing an electroconductive carbon black with a polyolefin resin. Some of these resins have been already practically used and, owing to the excellent electrical properties thereof, they are widely used as materials for various electric and electronic parts in a variety of appliance and automotive applications and the like. Recently, as electronic appliances have become highly advanced and highly accurate, there have been used integrated circuit, large-scale integrated circuit and, further, very-large-scale integrated circuit. In the case of parts of electronic appliances such as the above-noted integrated circuits or precision electric appliances, various problems such as electrostatic breakdown or attachment of dusts arise. In order to solve these problems, it was desired heretofore to develop a packaging material which does not bring about the electrostatic breakdown and which has moreover a cushioning capability. However, such a material has not been realized yet.
It is considered that this is due to the fact that a polyolefin resin comprising a large amount of carbon black has poor melt-viscoelasticity when molten and that it is therefore difficult for such a composition to maintain the closed cell internal gas pressure necessary for foaming, thereby resulting in impossibility of high expansion.
For instance, in Japanese patent application Laid-Open No. 47958/1973, there is disclosed a process for the manufacture of polypropylene resin foamed product containing carbon black. However, in lines 3-6 on page 5 of said publication, there is a description that an amount of the carbon black exceeding 0.1 weight part is not desirable because of the aggregation of cells during the growth thereof resulting in an undesirable increase of cell size.
A primary object of the present invention is to provide an electroconductive olefin polymer resin foamed product and, in particular, a foamed product suitable for use in packaging electronic appliance parts and the like which are sensitive to static electricity, in which case said foamed product should have a volume resistivity of 10.sup.8 .OMEGA..cm or less, preferably 10.sup.3 -10.sup.7 .OMEGA..cm is desirable. A further object of the present invention is to provide a composition of an olefin polymer resin which enables one to easily produce a low density foamed product having closed-cellular structure consisting of uniform-sized, fine cells, high cushioning capability and electroconductivity. Yet another object is to provide an olefin polymer resin composition from which there can be obtained an economically advantageous and electroconductive foamed product having a low volume resistivity in spite of a low ratio of electroconductive carbon black added to the resin.